Leveling

hey you guys i got my tank about a month and a half ago and before we put in the tank me and my friend leveled the tank. After we did we had his dad check to make sure it was level (his dad works in construction so this type of stuff is his thing) he said it was ok but after we got everything in sure enough the right side of my tank has about half of a centemeter less water then the left side. the level showed that the tank was level so i just want to know how major this is and if ican do anything about it.

sorry forgot to tell you guys its a 135 gallons

i dont know if i can but its worth a try am staying at my friends house today but i can tell you on monday after i get home from school and i did level it while there was no stuff inside

thanks danimal